In conventional exhaust silencers for vacuum cleaners, the noise is reduced by means of increasing the tortuosity of the airflow channel, i.e., by using labyrinthic airflow channels, to dissipate sound energy and by means of disposing porous sound-absorbing materials at the turning corners of the airflow channel to absorb sound energy. Poor noise silencing effect, however, is the main disadvantage of the above-mentioned silencing structures.